Society of human beings has entered into the age of technological industry as time goes on. In this age, a variety of technological products are inseparable from the lives of people. Among the technological products, vehicles are considered as important products in the age of technological industry because the vehicles are necessary tools for most people in daily lives. In fact, vehicles are constructed by using a variety of hardware components and software programs. When a vehicle engine is started by a user, the vehicle system would drive the loading procedures of a variety of software programs to be implemented such that the vehicle operates functionally. In traditional, a set of ACC cables must be disposed within the vehicle. The so-called ACC cables are used for controlling and activating functions of electronics control units (ECUs) (e.g. loading software programs into relative hardware components). As such, all of ECUs have to be connected to the set of ACC cables for activating the internal components within the ECU and turning off power consumptions of the components to avoid negative effects to the next engine start caused by running out of the vehicle battery. However, disposing the set of ACC cables would cause wastes of manpower and costs, and also occupies the internal rooms of the ECUs. An ideal and convenient engine-state detection device and method are provided in the present disclosure for the ECUs. Using the engine-state detection device and method does not require the set of ACC cables be connected to the ECUs and not to directly measure the DC voltage of the vehicle battery for determining the engine state.